u/KaleidoscopeOk4028

The one that always got me is uncompetitive. Competitive raising Km and noncompetitive dropping Vmax are easy enough to hold onto, but uncompetitive lowering both felt backwards until I understood why. The inhibitor only binds ES, so removing ES pulls the binding equilibrium forward and the enzyme looks like it grabs substrate more tightly, even though you have capped the ceiling.

I put all four side by side with what happens to Km, what happens to Vmax, and what the Lineweaver-Burk lines actually do, since that is usually the part a question is really testing.

The worked numbers on it use Km 25, Vmax 100 and an inhibitor at twice Ki, so you can see the apparent values rather than just the direction of travel.

Mixed inhibition is the one I am least confident about, since whether Km goes up or down depends on alpha and I have simplified that. If I have oversimplified anything else I would genuinely like to know. Last time I posted here eight people found things and the chart ended up much better for it.

Free and no signup: biochemtools.com/michaelis-menten-vs-lineweaver-burk.html

Only two of the twenty can't contribute to glucose at all, leucine and lysine, and they both start with L which is honestly the whole mnemonic. Everything else is either fully glucogenic or splits down both routes.

The bit I found genuinely surprising is that your body can't turn fat into sugar either, for the exact same reason. Both fat and those two amino acids end up as acetyl-CoA, and the step that makes it only runs one way. That's a big part of why prolonged fasting eventually starts eating into muscle, since amino acids are one of the last things left that can hold blood glucose up.

If anyone wants a closer look, this one and a bunch of other biochem charts are at biochemtools.com/charts.html. All free, no signup, and you're welcome to print them or drop them in a handout.

I went down a rabbit hole on ABO inheritance this week and ended up making this, mostly because I kept having to redraw the same Punnett square over and over to answer one question.

Laying all sixteen pairings out at once made a few things click that never did when I worked them one at a time. AB and O parents can never have an AB or an O child, which feels backwards until you write out the gametes. And A with B is the only pairing in the whole grid that can produce all four types, which I did not expect.

My favourite one is A with A though. Two type A parents really can have a type O child, because type A is either AA or AO and a blood test genuinely cannot tell you which. I imagine that has caused some awkward conversations over the years!

I wrote the impossible types into every cell too, since that is usually the part a question is actually testing.

Would love to hear if I have oversimplified anything, especially on the Rh side. It is free and there is no signup if anyone wants it: biochemtools.com/blood-type-punnett-square-calculator.html

I kept scanning down a table of pKa values and doing the plus or minus one in my head every time I needed to pick a buffer, so I laid them all out on a real pH axis instead. Each bar is the range where the buffer still has usable capacity, so you find your target pH and just look at what covers it.

A few things I did not expect once it was drawn this way:

Coverage is wildly uneven. Around pH 6.5 to 7.5 you have twelve options. Above pH 11 you have essentially one, phosphate's third pKa at 12.35. Everyone optimised for physiological pH and left the extremes alone.

10 of the 12 Good's buffers sit between pH 6 and 8.5, which makes sense given what Good was selecting for, but seeing them stack up in one band is different from reading it in a sentence.

Temperature is worse than I had internalised. Ammonium shifts 0.031 pH units per degree C and Tris 0.028, so a Tris buffer you set on the bench at 25 C is genuinely a different buffer once it is in a 4 C cold room. I flagged those in red.

It is completely free, no signup, and you can print it or drop it in a handout: biochemtools.com/buffer-pka-table.html

Would really appreciate it if you told me what you would change! I am not at a bench day to day, so I am sure there are practical things I have missed. Buffers that should be on here and are not, ones nobody actually uses any more, or cases where the plus or minus one rule is too generous.

Made this because every codon table I found was either a wall of grey text or locked in a textbook. Colour is by amino acid class, so you can see at a glance that the whole bottom-left block is nonpolar. AUG is marked as start, and the three stops are in red.

The thing that finally made the redundancy click for me: the third base barely matters for a lot of them. Every codon starting with CU is leucine no matter what comes third, and the same is true for valine, proline, threonine, alanine and glycine. That is why a mutation in the third position is so often silent.

Printable version and an interactive one where you click an amino acid to light up all its codons: biochemtools.com/codon-chart.html

I kept flipping between three different tables while studying amino acids, so I put everything on one page. All 20 grouped by side chain class, with both backbone pKa values, the side chain pKa where there is one, pI, molecular weight, Kyte-Doolittle hydropathy, and essential status.

The thing that finally made charge questions click for me: only 7 side chains ionize at all (D, E, H, C, Y, K, R). Those seven are the only ones that ever affect a protein's charge or pI. The other 13 are just along for the ride, and I wasted a lot of time treating them like they mattered.

pKa values are the Lehninger set. I also threw selenocysteine and pyrrolysine at the bottom since they come up as trivia, but they are not in the standard code so do not let them confuse you.

Hope it helps someone! Happy to fix anything that looks off.

I kept running into calculators that hand you a number and nothing else, which is useless when you're trying to learn the method or figure out whether you set the problem up wrong. So I started building ones that show every step.

There are 46 now. The ones that get used most:

• amino acid titration curves with the pKa regions and pI marked
• peptide net charge and pI from a sequence
• an amino acid chart with pKa, pI, MW and hydropathy, sortable and filterable
• enzyme kinetics, including what each inhibition type does to the curve
• an equation sheet where every formula links to the calculator that solves it

https://biochemtools.com

Free, no signup, no account needed. I recently added sources to the reference pages because it bothered me that most sites give you pKa values with no indication where they came from. Those now cite the Lehninger set for amino acid pKa, Kyte-Doolittle for hydropathy, and Good et al. for the buffer table.

If something obvious is missing, tell me and I'll add it.

I got annoyed that most free Tm calculators either ignore magnesium entirely or hide the thermodynamics, so I built one that does neither. Sharing it in case it's useful to anyone here.

https://biochemtools.com/dna-melting-temperature-calculator.html

What it does

• SantaLucia 1998 unified nearest-neighbor parameters
• Owczarzy 2004 monovalent and 2008 divalent salt corrections, picked automatically from the ratio of sqrt(Mg) to Na
• Solves for free Mg2+ after dNTP chelation instead of using the total, since that's usually what people get wrong
• Reports dH, dS, and dG37 next to the Tm with the full arithmetic shown
• Hairpin and self-dimer screen
• Buffer presets for PCR, qPCR, and Mg-free hybridization

What it doesn't do, so nobody wastes their time:

• No mismatches or dangling ends
• The dimer check counts base pairs, it doesn't compute a folding free energy
• No RNA or RNA/DNA hybrids
• IDT OligoAnalyzer is still better for primers you're actually ordering

I validated the whole pipeline against Biopython's Tm_NN and it agrees to 0.0 C across sodium-only, magnesium, dNTP, and self-complementary test cases. The thermodynamics also reproduces the published CGTTGA/TCAACG example from the SantaLucia paper exactly.

Free, no signup. If there's something obvious missing, tell me and I'll add it.

Surgeons practice on cadavers. Pilots practice in flight simulators. Sales reps practice on real customers — and lose real deals learning.

That always bothered me. So I built PrePitch.

It's an AI that role-plays as a difficult buyer and shows you exactly where you fold in a deal. Not a script generator, not a chatbot that tells you what to say. It watches your conversation and tells you where you caved on price, skipped the decision-maker question, or missed the moment the deal shifted.

I'm 17 and heading to UCLA in the fall. I got obsessed with the fact that every high-stakes profession has a way to practice except sales. So I spent the last few months building this.

Honest feedback from people who actually sell for a living would mean a lot. Does this solve a real problem? What's missing? What would make you actually use it?

Free to try, no credit card: prepitch.org